Hull for a Vessel

ABSTRACT

A hull is for a vessel and includes an elongated body rotatably connected to the vessel and a first end portion and a second end portion. The longitudinal axis of the elongated body substantially coincides with the longitudinal axis of the vessel and the elongated body is formed with a helical shape at least in a portion. The helical portion of the elongated body is provided with a star-shaped cross section.

FIELD

This invention relates to a hull for a vessel. More particularly, the invention relates to a hull including an elongated, helical body rotatably connected to the vessel.

BACKGROUND

When constructing a hull for a water-borne craft, for example a boat's hull, it is desirable that the hull should present as little resistance to motion as possible against the surrounding water mass. When the hull of a boat is moving in water, there are two main sources of resistance: frictional drag and wave resistance. The frictional drag arises on contact between water and the surface of the hull. At the hull, there will be a layer of water. Water that is in the immediate vicinity of the hull will be pulled together with the hull in the direction of motion of the hull. Water which is at a longer distance from the hull, for example several metres from the hull, will not follow the movement of the hull. The layer of water that follows the movement of the boat to a greater or lesser degree is called the boundary layer. The resistance involved in “pulling” this layer of water constitutes the frictional drag. Another source of resistance is the wave resistance. The wave resistance is, as a rule, the main source of the resistance to motion in water-borne craft. The wave resistance is connected to the energy needed to push away water when the hull is moving, and to the interaction between waves formed at the hull. Interference patterns between waves formed by the bow portion and the stern portion of the hull are particularly decisive of the magnitude of the wave resistance.

The greater the overall resistance to motion is, the more energy is needed to drive a water-borne craft forwards. By reducing the resistance to motion, it will be possible to use less fuel for propulsion at a particular speed. Reduced resistance to motion will also result in reduced fuel expenses and reduced emissions into the environment.

There is thus a need for new types of hulls which reduce the resistance to motion in water by the shape of the hull reducing the frictional drag and/or the wave resistance.

The following patent publications disclose vessels with hulls that may be considered as prior art relevant to the present invention:

-   -   GB 11699030 A;     -   U.S. Pat. No. 3,426,721 A;     -   U.S. Pat. No. 3,233,574 A; and     -   EP 0161198 A1.

Common to these patent publications is the fact that they describe water-borne craft with hulls including elongated, helical bodies facilitating the propulsion of the craft. One or more of the proposed helical elongated bodies are formed with flanges and/or circular portions which increase both the rotational resistance and the resistance to propulsion of the hull.

SUMMARY

The invention has for its object to remedy or reduce at least one of the drawbacks of the prior art or at least provide a useful alternative to the prior art.

The object is achieved through features which are specified in the description below and in the claims that follow.

The invention is defined by the independent claims. The dependent claims define advantageous embodiments of the invention.

In a first aspect, the invention relates to a hull for a vessel, the hull including an elongated body rotatably connected to the vessel and including a first end portion and a second end portion, the longitudinal axis of the elongated body substantially coinciding with the longitudinal axis of the vessel, and the longitudinal body being formed, at least in a portion, in a helical shape, characterized by the helical portion of the elongated body being provided with a star-shaped cross section. It will be understood that the hull may include one or more elongated helical bodies. Further the star-shape may be non-regular, as the two sides forming a point of the star may be of different lengths. One or both sides forming a point of the star may also be curved. This may be beneficial in order to reduce the resistance of the elongated body when it is moving in the water masses.

Preferably, the elongated body may also be formed with a plurality of openings connected, in terms of fluid, to a compression element. The compression element may be placed, for example, on the vessel or in a rotationally supported compartment in the elongated body. The compression element and the openings may be used to blow out air, or possibly some other fluid having a lower density than water, at the elongated helical body to reduce the pressure and thereby the friction on the elongated body. In a particularly advantageous embodiment, compressed air may be blown out of openings/nozzles on the low-pressure side in the helical grooves while the elongated body is rotating.

By means of modelling and experimental tests, the present applicant has concluded that in the elongated body, a star-shaped cross section gives a particularly low resistance to rotation and propulsion of the vessel while, at the same time, the elongated body may contribute to the buoyancy of the vessel.

In one embodiment, the star-shaped cross section may be provided with three or more points, preferably with four or more points and, in particular, preferably with five or more points. More points may give better buoyancy with the same diameter on the elongated body, and in advantageous embodiments, the elongated helical body may be formed with a cross section of a star with five or more points. The present applicant has performed successful tests with elongated helical bodies with cross sections of stars with as many as twelve points.

In one embodiment, the vessel may consist of a water-borne craft. Nevertheless, it will be understood that the present invention is not restricted to water-borne craft, but may also be used for other types of craft, such as airships and craft moving in snow or on ice.

In one embodiment, the elongated body may be a buoyancy body. The elongated body may thus contribute to the buoyancy of the craft. The elongated body may, in some embodiments, contribute to a substantial part of the buoyancy of the vessel. It may thus be an advantage if the elongated body is hollow, at least in a portion. In other embodiments, other parts of the hull may contribute more to buoyancy. It will also be understood that the elongated body may be a buoyancy body even if it is not hollow, as the elongated body may be provided in a material of a lower density than water, such as extruded polystyrene, expanded polystyrene or other porous polymer materials. The polymer material may in turn be covered with a composite material, such as a fibre-glass composite, so that a hard outer jacket is formed around the porous core.

In one embodiment, the elongated body may be provided with compartments. The elongated body may thus maintain a certain buoyancy even if one or more of the compartments are taking in water. Further, one or more of the compartments may be rotationally supported around the longitudinal axis of the elongated body, as rotationally supported compartments may be arranged not to follow the rotation of the elongated body, whereby rotationally supported compartments may be used as rooms for storing cargo and for passengers as well as for power supply and motors.

In an advantageous embodiment, the helical portion of the elongated body may include substantially the entire length of the elongated body. The above-mentioned advantages of the star-shaped cross section may thus be utilized to the full.

In one embodiment, the thread pitch of the helical portion may be at least one quarter of a turn over the length of the helical portion. Tests have shown, among other things, that a thread pitch of about half a turn over the length of the helical portion has given good results.

In one embodiment, the hull may further include a braking device arranged to brake the rotation of the elongated body. This may give a more controlled operation and simpler control and navigation of the vessel. There will typically be one or more braking devices known in the art, such as friction brakes or magnetic or electromagnetic brakes. The braking mechanism may also comprise an active brake which provides a reversal of the direction of rotation of the elongated body.

In one advantageous embodiment, the elongated body may be actively rotatably connected to the vessel. That implies the fact that the elongated body will function as a means of propulsion for the vessel. The elongated body will thus have to be connected to a motor which provides rotation. The elongated body may be the only means of propulsion of the vessel, or the elongated body may be used in combination with other known means of propulsion such as propellers, turbines, waterjets, air propellers or jet engines. Modelling carried out by the present applicant suggests that the abovementioned positive effects of a star-shaped cross section are greatest when there is active operation of the elongated body.

In an alternative embodiment, the elongated body may be connected to the vessel in a passively rotatable manner. This is to say, the vessel is provided with an alternative means of propulsion and the elongated body is just rotating along passively while the vessel is moving in the water masses.

A method of facilitating the propulsion of a vessel is described as well, the method including providing the vessel with a hull according to the first aspect of the invention, and propelling the vessel by means of the elongated, helical body.

In a second aspect, the invention relates to the use of an elongated helical body with a star-shaped cross section to reduce the resistance to propulsion of a vessel.

BRIEF DESCRIPTION OF THE DRAWINGS

In what follows, an example of one preferred embodiment is described, which is visualized in the accompanying drawings, in which:

FIG. 1 shows a vessel including a hull according to the present invention, in a side view;

FIG. 2 shows the vessel of FIG. 1, viewed in perspective;

FIG. 3 shows an elongated body as used in a hull according to the present invention, viewed in perspective;

FIG. 4 shows the elongated body of FIG. 4, viewed from above;

FIGS. 5A-C show different possible sections of an elongated body as used in a hull according to the present invention;

FIGS. 6A-D show different possible sections of an elongated body as used in a hull according to the present invention;

FIG. 7 shows a cross section of the elongated body of FIG. 4; and

FIG. 8 shows an alternative cross section of an elongated body as used in a hull according to the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

The figures are shown in a simplified and schematic manner, and details that are not important to highlight what is new about the invention may have been omitted from the figures. The various elements in the figures are not necessarily shown to scale relative to each other. Like or corresponding elements will be indicated by the same reference numeral in the figures.

Positional specifications such as “over”, “under”, “above”, “below”, “left” and “right” reflect the position shown in the figures.

In what follows, the reference numeral 1 indicates a hull for a vessel 10 according to the invention.

FIGS. 1 and 2 show a vessel 10 including a hull 1 according to the invention. The hull 1 includes four elongated bodies 3 having a first end portion 31 and a second end portion 33 and a length L1, as indicated in FIG. 3. The elongated bodies 3 constitute part of the hull 1 of the vessel 10. A compressor not shown is connected, in terms of fluid, to the elongated bodies 3 via a pipe connection 37, whereby compressed air can be blown out of openings 39 in the elongated bodies 3 as will be described with reference to FIG. 7 in what follows. The elongated bodies 3 are rotatably supported in guides 11 along the length of the hull 1. The actual supporting mechanism, which will typically include a bearing, is not shown in detail in the figures. On the deck of the hull 1, the vessel 10 is further provided with a superstructure 21, which is shown in a simplified and schematic manner in the figures. The elongated bodies 3 are driven by motors not shown, which may preferably be placed in the superstructure 21 of the vessel 10. Power from the motor for the rotation of the elongated bodies 3 may, for example, be transmitted by means of chains, not shown, extending around the supports in the guides 11. Alternatively, power may be transmitted via various gear assemblies.

FIGS. 3 and 4 show an example of an elongated helical body 3 which is part of a hull 1 according to the present invention. The elongated body 3 is formed with a helical shape with tapered end portions 31, 33. The elongated body 3 is further formed with five thread grooves 35, which gives the elongated body 3 a cross section in the shape of a five-point star, as shown in FIG. 7, FIG. 7 being a cross section viewed through the line A-A as indicated in FIG. 4. The thread pitch of the elongated body 1 is shown in FIG. 4 as somewhat more than a full turn over the length L1 of the device. In alternative embodiments, the thread pitch may be somewhat smaller, for example half a turn or less, per length of the elongated body 3. The thread pitch may conceivably be adapted and optimized relative to the desired forward speed of a vessel 10. It is conceivable that a smaller thread pitch, for example down to a quarter of a turn or less, will be preferable at higher forward speeds of the vessel 10.

In the figures, the elongated body 3 is shown as a continuous unit, but it will be understood from the invention that the elongated body 3 may be formed from several parts joined together.

FIGS. 5A-5C show sections through conceivable elongated bodies 3, not shown, of alternative cross-sectional shapes, shown here as six-, four- and three-point stars, respectively.

FIGS. 6A-D show different cross sections of conceivable elongated bodies 3, not shown, provided with compartments 15. It is thus achieved that the buoyancy of the elongated body 3 is maintained even if one or more compartments 15 is/are taking in water. The elongated bodies 3 shown in FIGS. 6A-6B may, for example, consist of an assembly of metal plates joined together. It is further conceivable that the circular compartment 15 as shown in FIG. 6B may be rotationally supported around the longitudinal axis A1 of the elongated body. It is thereby achieved that the compartment 15 will not follow the rotation of the elongated body, and the compartment 15 may thereby conceivably be arranged as a hold, a passenger cabin or as a room which may house power-supply units and/or motors. It is further conceivable that the elongated body 3 may be divided along its longitudinal axis A1 so that the elongated body 3 may be opened for access to at least one of the rotationally supported compartments 15 to be obtained.

In FIGS. 5A-C and FIGS. 6A-D it is indicated that the elongated body is hollow, but it will be understood from the invention that the elongated body 3 may consist of any material which may ensure the necessary buoyancy of the vessel 10 as mentioned above.

FIG. 7 shows a cross section of the elongated body 3 as shown in FIGS. 3 and 4, seen through the lines A-A in FIG. 4. The central channel 37 is an extension of the air channel 37 as shown in FIGS. 1 and 2 and connects an air compressor, not shown, to openings/nozzles 39 in the surface of the elongated body 3. Through the openings 39, compressed air may be blown out, contributing to reducing the frictional drag of the elongated body 3 when it is rotating and moving in the water masses. The direction of rotation of the elongated body 3 is indicated by an arrow in the figure. In rotation, a high-pressure side Hp and a low-pressure side Lp are formed at each of the points of the star-shaped cross section of the elongated body. Modelling carried out by the present applicant has shown that, in operation, blowing out compressed air may, to a substantial degree, reduce the frictional drag. In what follows, an exemplary embodiment will be described, from which the drag-reducing effect of the device will appear.

FIG. 8 shows a cross section of an elongated body 3 with an alternative, non-regular star shape. As it can be seen from the figure, each of the four points has been formed in such a way that the high-pressure side Hp is short and straight, whereas the low-pressure side Lp has been extended and arched. The direction of rotation of the elongated body is indicated by an arrow in the figure. In an alternative embodiment not shown, the low-pressure side Lp of each point may be straight instead of curved. The channel 37 and openings 39 for blowing out air on the low-pressure side Lp are also indicated in the figure.

In a watercourse 8.28 m in length, two plastic models of a vessel according to the invention (the test model) and a model of a vessel with a common boat's hull (the reference model), respectively, were placed. Both vessels were made by means of three-dimensional printing and were made from a plastic material. The test model was formed as shown in FIG. 3 and provided with two helical bodies according to the invention. The test model was not provided with means of propulsion 23, as is shown in FIG. 3. The helical bodies of the test model were suspended by ball bearings at their end portions.

The test model and the reference model weighed 300 grams and 298 grams, respectively.

To pull the models in the watercourse, the models were attached to a line at their bow portions. The line was attached, at its other end, to a weight element and placed in a pulley system. A pulling force was transmitted to the models by dropping the weight element from a height of 8.28 m above the ground. Weight elements of two different weights were used in the different test series. The weight elements were 214 grams and 499 grams, respectively.

In a first test, the helical bodies were positioned in such a way that the directions of rotation of both helical bodies were in towards the vessel. The weight that was used weighed 214 grams. Two parallel experiments were conducted, in which the time that the models took to cover the distance of 8.28 metres was measured.

Test 1:

Experiment 1.1: Test model 4.63 sec., Reference model 6.30 sec.

Experiment 1.2: Test model 4.87 sec., Reference model 6.27 sec.

In a second test, a corresponding test setup to that of test 1 was used, but the helical bodies were disposed with a direction of rotation away from the vessel. Four parallel experiments were conducted.

Test 2:

Experiment 2.1: Test model 4.40 sec., Reference model 6.37 sec.

Experiment 2.2: Test model 4.43 sec., Reference model 6.43 sec.

Experiment 2.3: Test model 4.23 sec., Reference model 6.20 sec.

Experiment 2.4: Test model 4.32 sec., Reference model 6.33 sec.

In a third test, a corresponding test setup to that of test 2 was used, but the weight of the weight element was 499 grams. Four parallel experiments were conducted.

Test 3:

Experiment 3.1: Test model 2.27 sec., Reference model 5.07 sec.

Experiment 3.2: Test model 2.16 sec., Reference model 4.97 sec.

Experiment 3.3: Test model 2.09 sec., Reference model 4.96 sec.

It was concluded from the experimental results that the test model with helical bodies exhibited substantially less resistance to motion than the reference model which was provided with a common boat's hull. It was also observed that there was considerably less wave formation when the model with the helical bodies was moving than when the reference model was moving.

It is not known what is the exact mechanism behind the reduced resistance to propulsion, but it is conceivable that when helical bodies are used, both the frictional drag and the wave resistance are substantially lower than when conventional boat hulls are used. A surprising effect of the device according to the invention has thus been demonstrated. 

1-14. (canceled)
 15. A hull for a vessel, the hull including an elongated body rotatably connected to the vessel and including a first end portion and a second end portion, the longitudinal axis of the elongated body substantially coinciding with the longitudinal axis of the vessel and the elongated body being formed with a helical shape at least in a portion, wherein the helical portion of the elongated body is provided with a star-shaped cross section.
 16. The hull according to claim 15, wherein said star-shaped cross section is provided with three or more points.
 17. The hull according to claim 15, wherein the vessel is a waterborne craft.
 18. The hull according to claim 15, wherein the elongated body is a buoyancy body.
 19. The hull according to claim 15, wherein the elongated body is hollow.
 20. The hull according to claim 15, wherein the elongated body is provided with compartments.
 21. The hull according to claim 20, wherein at least one of the compartments is rotationally supported around the longitudinal axis of the elongated body.
 22. The hull according to claim 15, wherein the helical portion of the elongated body includes substantially an entire length of the elongated body.
 23. The hull according to claim 15, wherein a thread pitch of the helical portion is at least a quarter of a turn over the length of the helical portion.
 24. The hull according to claim 15, wherein the elongated body is provided with a braking device.
 25. The hull according to claim 15, wherein the elongated body is actively rotatably connected to the vessel, whereby the elongated body works as a means of propulsion for the vessel.
 26. The hull according to claim 15, wherein the elongated body is passively rotatably connected to the vessel.
 27. The hull according to claim 15, wherein the elongated body is formed with a plurality of openings connected, in terms of fluid, to a compression element.
 28. A vessel having a hull, an elongated body rotatably connected to the vessel, and a first end portion and a second end portion, the longitudinal axis of the elongated body substantially coinciding with the longitudinal axis of the vessel and the elongated body being formed with a helical shape at least in a portion, wherein the helical portion of the elongated body is provided with a star-shaped cross section. 